Nowadays, optical parts, such as lenses made from inorganic glass, are frequently replaced by organic resins in view of good workability, light weight, low cost, high resistance to impacts, and other useful properties inherent in the aforementioned organic materials. In response to recent miniaturization of optical elements, intensification of light sources along with increase in working temperatures and light intensities, a demand occurred for development of new organic resin materials that would possess high resistance to heat and light. On the other hand, it is well known that silicone resins are characterized by excellent resistance to heat, excellent resistance to low temperatures and such properties as excellent electrical insulating characteristics, water repellency, transparency, etc. Therefore, curable silicone resin compositions find application in various fields of industry. Moreover, it is expected that, due to color stability and the ability of maintaining better physical properties than other organic resin materials, silicone resin compositions will find wider use as a material for manufacturing optical elements.
Curable silicone resin compositions, and among them, in particular, curable organopolysiloxane resin compositions such as addition-curable organopolysiloxane resin compositions, are characterized by good curability, rapid curing, and absence of by-products.
For example, Japanese Patent Publication (Kokoku) No. S52-44900 (that corresponds to U.S. Pat. No. 3,732,330) discloses an addition-curable silicone resin composition that is comprised of a methylphenylvinylpolysiloxane resin composed of C6H5SiO3/2 units and CH2═CH(CH3)2SiO1/2 units, di(dimethylhydrogensiloxy)diphenylsilane represented by the following formula: [H(CH3)2SiO]2Si(C6H5)2, and a platinum catalyst.
Japanese Unexamined Patent Application Publication (hereinafter referred to as Kokai) No. S53-20545 discloses a curable organopolysiloxane resin composition that is comprised of a methylphenylvinylsiloxane resin composed of monophenylsiloxane units, diphenylsiloxane units, dimethylsiloxane units, and vinylmethylsiloxane units, a linear-chain methylphenylhydrogenpolysiloxane composed of diphenylsiloxane units, methylhydrogensiloxane units, dimethylsiloxane units, and trimethylsiloxane units, and a platinum catalyst. The above materials are used as coating agents, moldable resins, and encapsulators for electronic parts. Furthermore, Kokai 2002-265787 describes an addition-curable silicone resin composition that consists of an organopolysiloxane resin that contains phenyl and alkenyl groups, a phenyl containing organohydrogenpolysiloxane, and a hydrosilation-curing catalyst. Cured bodies produced from the last-mentioned composition possess high transparency, strength, and hardness, and therefore find application for manufacturing parts of electronic and electrical devices, office-automation machines, and precision instruments.
However, a methylphenylpolysiloxane resin is normally in a solid or in a highly viscous liquid state and, therefore, it does not possess satisfactory moldability and flowability. Thus, Kokai S54-159459 (that corresponds to U.S. Pat. No. 4,234,713) describes an addition-curable organopolysiloxane resin composition which is comprised of a methylphenylvinylpolysiloxane resin composed of C6H5SiO3/2 units and CH2═CH(CH3)2SiO1/2 units, a dimethylhydrogensiloxyphenylsilane composed of units expressed by formulae [H(CH3)2SiO]2Si(C6H5)2 or [H(CH3)2SiO]3Si(C6H5), and a platinum catalyst with an addition of a diluent in the form of a diphenylbis(dimethylvinylsiloxy)silane. Practical Example No. 1 of Kokai H11-1619 discloses an addition-curable organopolysiloxane resin composition, which is comprised of a methylphenylvinylpolysiloxane resin, methylphenylhydrogenoligosiloxane, and a platinum catalyst with an addition of a disiloxane of the following formula: [CH2═CH(CH3)2Si]2O.
However, the aforementioned patent references do not show curable organopolysiloxane compositions or addition-curable silicone resin compositions capable of preserving their hardness at high temperatures. If a cured body looses its hardness at high temperatures, it becomes unsuitable for use as an optical material. For example, when an optical lens is located in a vicinity of a light-emitting element, or when the resin is used as a sealant, coating agent, or an adhesive substance and operates near a highly intensive light source, such optical elements and agents may be subject to thermal deformations.